sql - max from group flag setter - sql

Question

I m trying to achieve flag setting for the condition in my table below
p_id mon_year e_id flag
---- --------- ----- -----
1 2011/11 20 0
1 2011/11 21 1
1 2012/01 22 1
1 2012/02 23 0
1 2012/02 24 0
1 2012/02 25 1
2 2011/11 28 0
2 2011/11 29 1
2 2012/01 30 1
grouping by p_id,e_id and mon_year, the flag is set for the last value in the month.
I m confused how can i achieve this
I tried to achieved this by using row_number and partition to seperate out the value. By still looking for to achieved
Output by using row_number query , i have got is as below:
Grouping by
p_id mon_year e_id row
---- --------- ----- -----
1 2011/11 20 1
1 2011/11 21 2
1 2012/01 22 1
1 2012/02 23 1
1 2012/02 24 2
1 2012/02 25 3
2 2011/11 28 1
2 2011/11 29 2
2 2012/01 30 1
Max of this value would set the flag column. But i m really bugged how to achieve it. Any help would be useful.
Thanks !!

Answer 1

I think this is what you're going for. . . The output exactly matches your example:
declare #t table (p_id int, [year] int, [month] int, [day] int)
insert #t select 1, 2011, 11, 20
union select 1, 2011, 11, 21
union select 1, 2012, 01, 22
union select 1, 2012, 02, 23
union select 1, 2012, 02, 24
union select 1, 2012, 02, 25
union select 2, 2011, 11, 28
union select 2, 2011, 11, 29
union select 2, 2012, 01, 30
select p_id, [year], [month], [day]
, case when r=1 then 1 else 0 end flag
from
(
select p_id, [year], [month], [day]
, row_number() over (partition by p_id, [year], [month] order by [day] desc) r
from #t
) x
order by p_id, [year], [month], [day]
Output:
p_id year month day flag
1 2011 11 20 0
1 2011 11 21 1
1 2012 1 22 1
1 2012 2 23 0
1 2012 2 24 0
1 2012 2 25 1
2 2011 11 28 0
2 2011 11 29 1
2 2012 1 30 1

Answer 2

Try ordering by descending. In that way, you don't have to look for maximum ROW_NUMBER but when ROW_NUMBER is 1 ;)
Something like this (I didn't completely understand what you want to achieve, so this is probably not 100% accurate):
WITH r_MyTable
AS
(
SELECT
*,
ROW_NUMBER() OVER (PARTITION BY mon_year ORDER BY p_id, e_id DESC) AS GroupRank
FROM MyTable
)
UPDATE r_MyTable
SET flag = CASE WHEN GroupRank = 1 THEN 1 ELSE 0 END;

Answer 3

You can use max statement on e_id to get last value for the month, code is below:
IF OBJECT_ID('tempdb..#tmptest') IS NOT NULL
DROP TABLE #tmptest
SELECT
*
INTO
#tmptest
FROM
(
SELECT '1' p_id, '2011/11' mon_year, '20' e_id, '0' flag UNION ALL
SELECT '1', '2011/11', '21', '1' UNION ALL
SELECT '1', '2012/01', '22', '1' UNION ALL
SELECT '1', '2012/02', '23', '0' UNION ALL
SELECT '1', '2012/02', '24', '0' UNION ALL
SELECT '1', '2012/02', '25', '1' UNION ALL
SELECT '2', '2011/11', '28', '0' UNION ALL
SELECT '2', '2011/11', '29', '1' UNION ALL
SELECT '2', '2012/01', '30', '1'
) as tmp
SELECT
tmptest.*
FROM
(
SELECT
MAX(e_id) e_id
,p_id
,mon_year
FROM
#tmptest
GROUP BY
p_id,mon_year
) tblLastValueEID
INNER JOIN
#tmptest tmptest
ON
tmptest.p_id = tblLastValueEID.p_id
AND
tmptest.mon_year = tblLastValueEID.mon_year
AND
tmptest.e_id = tblLastValueEID.e_id